Process for the purification of



United States Patent 3,150,193 PROCESS FOR THE PURIFICATION OF ALKANOLS Jerry A. Acciarri and Donald R. Napier, Ponea City, Okla, assignors to Continental Oil Company, Ponca City, Gkltb, a corporation of Delaware No Drawing. Filed Jan. 14, 1960, Ser. No. 2,325 14 Claims. (Cl. 260-643) This invention relates to a process for the separation and recovery of alkanols from admixture with alkanes and alkenes by extractive crystallization with nitroalkanes.

In the preparation of alkanols, for example, by the oxidation of aluminum trialkyls followed by hydrolysis of the alkoxy product, compounds are produced which cannot be separated economically by simple fractionation alone because of the proximity of the boiling points, particularly of the higher molecular weight components.

It is an object of this invention to provide an improved process for the separation of alkanols from complex admixtures comprising alkanes and alkenes.

Another object of this invention is to provide an improved process for separating C-12 and higher alcohols from admixture with n-alkanes and l-alkenes of similar boiling points.

Still another object of this invention is an improved process for the recovery of alcohols from reaction product obtained by the oxidation and hydrolysis of trialkyl-' aluminum compounds.

These and other objects of the invention will become more readily apparent from the following detailed description and discussion.

The foregoing objects are achieved broadly by subjecting a mixture comprising alkanols, alkanes and alkenes to extractive crystallization with a nitroalkene and recovering an alcohol product.

In one aspect of the invention the nitroalkane is added to said mixture, thereafter the temperature of the mixture is reduced until alkanols crystallize from solution, the crystals are separated by filtration and treated to remove residual nitroalkane and olefin.

In another aspect of the invention said mixture is reduced in temperature until alkanois crystallize from solution, the nitroalkane is added to liquid-crystal mixture and the mixture agitated, allranol crystals are separated by filtration and the separated crystals are treated to remove residual nitroalkanes and olefins.

In each of the specific embodiments above, treating of the crystals can be either by stripping or by water washing.

The process of this invention is broadly applicable to the separation and recovery of allcanols from admixtures comprising alkanes and alkenes. The process finds particular application in the treatment of admixtures of similar boiling points which cannot be economically separated by distillation. The invention finds special use in the separation and recovery of alkanols prepared from the oxidation and subsequent hydrolysis of complex metal alkyls, e.g., aluminum triaikyls, as described in United States Patent 2,892,858 to Karl Ziegler. Briefly,in this process a simple metal alkyl, such as aluminum triethyl, is grown (reacted) continuously with an olefin, such as ethylene, whereby complex metal alkyls are formed. The complex metal alkyls are then oxidized with oxygen (air) to form metal alkoxy compounds. Hydrolysis of the alkoxy compounds provides a mixture of alcohols, olefins, paratfins and minor amounts of oxygenated compounds, such as aldehydes. The alcohols which are formed in this reaction have a composition following a Poisson distribution and ranging from ethanol to l-tetracosanol.

3,150,193 Patented Sept. 22, 1964 The lower molecular weight alcohols up through those containing about 10 carbon atoms are readily separable by distillation. However, the higher molecular weight compounds containing from about 12 to about 22 carbon atoms and including alkanols and l-alkenes and n-alkanes are sufficiently close in boiling points that their separation by distillation is impractical. The boiling points of a representatve mixture are listed below:

In carrying out the invention in one embodiment, for example for the recovery of alkanols from an admixture such as that listed above, a nitroalkane such as nitroethane is first added to said mixture. The mixture is thereafter reduced in temperature until alkanols crystallize from solution. The crystals are separated from the liquid and are treated to remove residual nitroethane and other components, principally olefins. The reaction conditions employed in this process can vary substantially depending on the particular components in the mixture to be treated, the specific nitroalkane which is employed in effecting the separation and on the particular manner in which the steps of the process are carried out. For example, when separating alkanols containing from about 12 to about 24 carbon atoms utilizing nitroethane, crystallization of the alkanols can be efiected at about to about F. When utilizing other nitroalkanes either higher or lower temperatures are required, depending on the particular extracting agent employed. Thus nitropropane requires lower temperatures than nitroethane and crystallization of the alkanols can be effected at higher temperatures with nitromethane. Preferably the nitroalkane and alkanol-alltane-alkene mixture are agitated prior to crystallization and if necessary can be heated to provide a single phase during this operation. The alcohol crystals can be separated from the mixture by any suitable means, for example, filtration, centriiugation, etc. Because of the viscosity of the mixture it is desirable that this separation be effected under a vacuum, preferably in the order of about to about 600 millimeters of mercury. The alcohol crystals, while substantially richer in alcohol content than the original mixture, contain residual amounts of nitroalkane and other components, principally olefins. Crystals can be further purified by a subsequent treatment which can include either stripping or water washing. In view of the boiling points of the materials emplo 'ed further treatment by stripping is desirably carried out under a low vacuum, usually in the order of between about 5 and about 100 millimeters of mercury. Although not usualiy required an extraneous stripping gas which is inert in the system, such as nitrogen, can be used if desired.

The extraction agent employed in the process comprises the lower nitroalkanes, preferably nitrornethane, nitroethane and nitropropane. These materials can be used singularly or in combination. The particular extractive agent employed depends on the mixture which is to be treated. As pointed out previously the conditions of temperature, pressure, etc., which are provided depend on the composition of the mixture of alcohols, alkanes and alkenes and also on the particular extraction agent i which is used. The nitroalkane is used ordinarily in an amount varying from between about 0.25 and about 20 grams per gram of alcohol-alkene-alkane mixture and preferably between about 1 and about grams per gram.

The metal alkyls from which the alkanols are prepared can contain various metals, particularly those in Groups I, II and III of the Periodic Table, such as sodium, boron, magnesium, aluminum, lithium and the like. Of the metal alkyls, however, the aluminum trialkyls are preferred and are those generally employed.

In another embodiment of the invention involving a somewhat difierent order of steps, a mixture of alkanols, alkanes and alkenes is first subjected to a temperature reduction suflicient to provide crystallization of alkanols from solution. Following this nitroalkane is added to the solids liquid mixture followed by agitation, after A similar procedure, as Example 1, was used with the exception that a 5/1 weight ratio of nitroethane to alcohol-olefin mixture was used.

EXAMPLE 3 A similar procedure and starting mixture, as Example 1, was used with the exception that at 2/1 weight ratio Which lhe llqulds and 301155 are sePamied by filtrfmon h 0t nitroethane to alcohol-olefin mixture was used; and the elthef h pp of Water d remove f alcohol rich layer filter cake was washed with six times purities trom the alcohol crystals. The conditions emits Weight f 40 waten ployed in this process, for example, temperatures, pressures, quantities of nitroalkane, etc., are substantially the EXAMPLE 4 same as those used in the preceding embodiment of the A similar procedure as Example 1 was used, with the invention. exception that a 1/1 weight ratio of nitroethane to al- Both embodiments of the invention can b practiced cohoholefin mixture was used. The results obtained in to recover substantially pure alcohols from a complex each of the Examples 1-4 are presented in Table I. mixture. The degree of purity of the product is of course dependent both on the conditions employed in the process EXAMPLE 5 and on the number of stages of separation which are car- A 248.4 gram hhXhlfe 0f alcohol-Olefin and 1242 grams ried out. The latter are readily determined by those of nitroethane were mixed for 10 minutes at 42 F. The skilled in the art from a consideration of the selectivity COmPOSifiOH 0f the alcohol-Olefin tart ng mixt r Was values obtained in a single stage separation, selectivity 0 as w 1' W ght percent l-dodecauol, 57.3 Weight being defined as set forth in Tables I and II hereafter P@l'CeI1ll 1-tetIadeCah01, Weight Percent l-heXadecahol, presented. It is contemplated that in a multi-stage separa- 3.8 Weight P h l-heXadeceIle, Wight Percent tion recycle of products obtained from the various stages h h The llquid-sohd were then Separated y can be practiced in a conventional manner and also heat hahoh Into 1226-4 grams Ilitmethahe rich layer and exchange between the various streams for the conserva- 21 264-0 grams 0f a1 c0h01 Tich y The Ilitfoethane tion d imu utili tio f energy (38.0 grams) was stripped from the alcohol rich layer at While in the preferred embodiment the invention is di- 8 IIlIhg absolute Pressihre and rected to the treatment of mixtures containing n-alkanols, EXAMPLE 6 n-alkanes and l-alkenes, it is within the scope of the invention to separate more complex materials, such as 4.0 A slmllar Procedure as in Example 5 was usei branched alkanols and alkanes and internally unsaturated EXAMPLE 7 olefins, and various combinations thereof. A H d E 1 5 The following examples are presented in illustration m prose as 6 W used l the exception that a 2/1 welght who of nitroethane alof the mventlon. h 1 1 fin d EXAMPLE 1 co o-oe mix ure was use A 241.1 gram alcohol-olefin mixture was mixed with EXAMPLE 8 487 grams of nitroethane. (The composition of the orig- A similar procedure, as in Example 5, was used with inal alcohol-olefin mixture was as follows: 0.9 weight perthe exception that a 10/ 1 weight ratio of nitroethane to Table 1 Weight Percent Weight Original Impurities Weight Percent Original Alcohol Ratio, Mixing Crystalli- Removed From Recovered as Product Example Nitro Temp., zation Alcohols Selectivity Remarks N 0. ethane/ 0. Temp,

Alcohol C.

l-Hexa- I-Octa- 0 20B 0 4011 01 011 decene decene 1 2/1 5 35. 2 17. 9 68. 2 90. 0 94. 0 1. 3 2 5/1 50 5 49. 1 26.3 100. 0 90. 0 100. 0 1. 5 3 2/1 50 5 45.0 31.0 48.3 97.6 95.4 1.5 (Alcohol crystals washed with 6 vgggngs of water 4 1/1 50 5 16.2 11.3 59.5 100.0 100.0 1.2 a

Definition of Selectivity (B):

Wt. percent alcohol in final product Wt. percent impurities in final product where n=N umber contacting stages.

Wt. percent alcohol in initial mixture Wt. percent impurities in initial mixture alcohol-olefin mixture was used.

EXAMPLE 9 A similar procedure, as in Example 8, was used with the exception that the alcohol mixture composition was as follows: 0.97 weight percent l-dodecanol, 41.99 weight percent l-tetradecanol, 28.52 weight percent l-hexadecanol, 13.47 weight percent l-octadecanol, 2.79 Weight percent l-hexadecene, 5.83 weight percent l-octadecene, 3.52 weight percent .n-eicosane and 2.91 weight percent 4. The process for the separation of alkanols from a liquid mixture obtained from the oxidation and subsequent hydrolysis of complex aluminumtrialkyls, said mixture consisting essentially of l-docecanol, l-tetradecanol, l-hexadecanol, l-hexadecene and l-octadecene which 5 n-docosane. comprises adding to said mixture from about 1 to about The results obtained in each of the Examples 5-9 are 5 parts of nitroethane per part of said mixture, agitating presented in Table II. the mixture, thereafter adjusting the temperature of said Having thus described the invention by providing spemixture to w1thin the range from about 35 to about 55 F. cific examples thereof, it is to be understood that no un- 10 until alkanols crystallize from solution, separating said due limitations or restrictions are to be drawn by reason crystals by vacuum filtratlon and washing said crystals thereof and that many variations and modifications are with water to remove residual nitroethane and alkenes. within the scope of the invention. 5. A process for the separation of alkanols from a Table II Weight Weight Percent Original Impurities Removed Weight Percent of Original Alcohol Recovered Ratio, as Product Example Ntro- Temp, Selectivity t le h l l-Hexal-Octan-eicon-doco- Ctr-20H 014011 0 6GB 0 GB decene dceenc sane sane /1 5 21. 0 2,17 4 92. o 93. 7 1. 3 5/1 5 20. 0 25. 6 100. 0 9s. 2 1. 2 2/1 5 10. 0 22. 0 100.0 99. s 1. 2 10/1 5 27. 9 37. s 78. 6 9o. 8 1. 4 10/1 5 10.7 39. 2 62. 5 83. 2 1. 3

Definition oi Selectivity (13):

Wt. percent alcohol in final product Wt. percent impurities in final product where n=Numher contacting stages It is noted from the examples that extractive fractionation with nitroethane, even in a single stage, provides an alcohol product of substantially improved purity.

We claim:

1. A process for the separation of alkanols containing from about 12 to about 24 carbon atoms from a liquid mixture consisting essentially of said alkanols and al'xanes and mono-olefins of similar boiling points which comprises adjusting the temperature of said mixture to within the range from about 35 to about 55 F. until alkanols crystallize from solution, thereafter adding to said mixture containing crystals from about 0.25 to about parts of nitroethane per part of said mixture, subjecting the mixture containing crystals and nitroethane to agitation, separating said crystals and Washing the separated crystals with water to remove residual nitroethane and monoolefins.

2. A process for the separation of alkanols from a liquid mixture obtained from the oxidation and subsequent hydrolysis of complex aluminumtrialkyls, said mixture consisting essentially of l-docecanol, l-tetradecanol, l-hexadecanol, l-hexadecene and 1-0ctadecene which comprises adding to said mixture from about 0.25 to about 20 parts of nitroethane per part of said mixture, subjecting the mixture to agitation, thereafter reducing the temperature of said mixture to within the range from about to about 55 F. until alkanols crystallize from solution, separating said crystals by vacuum filtration and stripping said crystals to remove residual nitroethane and alkenes.

3. A process for the separation of alkanols from a mixture obtained from the oxidation and subsequent hydrolysis of complex aluminumtrialkyls, said mixture consisting essentially of l-docecanol, l-tetradecanol, l-hexadecanol, l-octadecanol, l-hexadecene, l-octadecene, n-eicosane and n-docosane which comprises adding to said mixture from about 1 to about 5 parts of nitroethane per part of said mixture, agitating the mixture and heating to provide a single phase, thereafter adjusting the temperature of said mixture to within the range from about 35 to about 55 F. until alkanols crystallize from solution, separating said crystals by vacuum filtration and stripping said crystals under vacuum to remove residual nitroethane and alkenes.

Wt. percent alcohol in initial mixture 08) (Wt percent impurities in initial mixture mixture obtained from the oxidation and subsequent hydrolysis of complex aluminumtrialkyls, said mixture consisting essentially of l-docecanol, l-tetradecanol, 1hexa decanol, l-octadecanol, l-hexadecene, l-octadecene, neicosane and n-docosane which comprises adding nitroethane to said mixture in an amount of from about 0.25 gram of the nitroethane per gram of the mixture to about 20 grams of nitroethane per gram of the mixture, agitating the resulting mixture and heating to provide a single phase, thereafter reducing the temperature of said resulting mixture to within the range from about 35 to about F. until alkanols crystallize from solution, separating said crystals from the resulting mixture by vacuum filtration and washing said crystals with Water to remove residual nitroethane and alkenes.

6. A process for the separation of alkanols from a liquid mixture obtained from the oxidation and subsequent hydrolysis of complex aluminumtrialkyls, said mixture consisting essentially of l-docecanol, l-tetradecanol, l-hexadecanol, l-hexadecene and l-octadecene which comprises adjusting the temperature of said mixture to within the range from about 35 to about 55 F. until alkanols crystallize from solution, thereafter adding to said mixture from about 1 to about 5 parts of nitroethane per part of said mixture containing crystals subjecting the mixture containing crystals and nitroethane to agitation, separating said crystals by filtration and stripping said crystals to remove residual nitroethane and alkenes.

7. A process for the separation of alkanols containing from about 12 to about 24 carbon atoms from a liquid mixture consisting essentially of said alkanols and alkanes and mono-olefins of similar boiling points which comprises adding to said mixture from about 0.25 to about 20 parts by weight of a lower nitroalkane having up to three carbon atoms per molecule per part by Weight of said mixture, subjecting the resulting mixture to agitation, thereafter reducing the temperature of said resulting mixture to within the range from about 35 to about 55 F. until alkanols crystallize from solution, separating said crystals from the resulting mixture and stripping the separated crystals to remove residual nitroalkane and alkenes.

8. The process of claim 7 in which said mixture is hgated prior to crystallization to provide a single liquid p ase.

9. A process for the separation of alkanols containing from about 12 to about 24 carbon atoms from a mixture consisting essentially of said alkanols and alkanes and mono-olefins of similar boiling points which comprises adding to said mixture from about 1 to about 5 parts by Weight of nitroethane per part by weight of said mixture, agitating the resulting mixture and heating to provide a single phase, thereafter reducing the temperature of said resulting mixture to Within the range from about 35 to about 55 F. until alkanols crystallize from solution, separating said crystals from the resutling mixture by vacuum filtration and stripping the separated crystals under vacuum to remove residual nitroethane and alkenes.

10. A process for the separation of alkanols containing from about 12 to about 24 carbon atoms from a liquid mixture consisting essentially of said aikanols and alkanes and mono-olefins of similar boiling points which cmprises adding to said mixture from about 0.25 to about 20 parts by Weight of nitroethane per part by weight of said mixture, thereafter reducing the temperature of the resulting mixture to within the range from about 35 to about 55 F. until alkanols crystallize from solution, separating said crystals from the resulting mixture and washing the separated crystals with water to remove residual nitrcethane and mono-olefins.

11. The process of claim 10 in Which said mixture is heated prior to crystallization to provide a liquid single phase.

12. A process for the separation of alkanols containing from' about 12 to about 24 carbon atoms from a mixture consisting essentially of said alkanols and alkanes and mono-olefins of similar boiling points which comprises adding to said mixture from about 1 to about parts by weight of nitroethane per part by Weight of said mixture, agitating the resulting mixture and heating to provide a single phase, thereafter reducing the temperature of said resulting mixture to Within the range from about 35 to about 55 F. until alkanols crystallize from solution, separating said crystals from the resulting mixture by vacuum filtration and washing the separated crystals with water to remove residual nitroethane and mono-olefins.

13. A process for the separation of alkanols containing from about 12 to about 24 carbon atoms from a liquid mixture consisting essentially of said alkanols and alkanes and mono-olefins of similar boiling points which comprises adjusting the temperature of said mixture to within the range from about to about F. until alkanols crystallize from solution, thereafter adding to said mixture from about 0.25 to about 20 parts by weight of nitroethane per part by weight of said mixture, subjecting the resulting mixture containing crystals and nitroethane to agitation, separating said crystals from the resulting mixture and stripping the separated crystals to remove residual nitroethane and mono-olefins.

14. A process for the separation of alkanols from a liquid mixture consisting essentially of said alkanols having from about 12 to about 24 carbon atoms, n-alkanes and mono-olefins which comprises adjusting the temperature of the liquid mixture until the alkanol crystallize, adding to the mixture from about 0.25 to about 20 parts by weight of a lower nitroallcane per part by Weight of said mixture and separating the alkanol crystals from the resulting mixture.

References Cited in the file of this patent UNITED STATES PATENTS 2,113,960 Grote et a1. Apr. 12, 1938 2,479,041 Elgin Aug. 16, 1949 2,629,686 Grosser Feb, 24, 1953 2,700,049 Rottig Jan. 18, 1955 OTHER REFERENCES Scheflan et al.: The Handbook of Solvents, D. Van Nostrand Company Inc., New York (1953), page 558. (Copy in Library.)

Ashley: Fette, Seifen, Anstrichmittel, 58, 535-8 (1956) (Copy in Scientific Lib.) 

7. A PROCESS FOR THE SEPARATION OF ALKNAOLS CONTAINING FROM ABOUT 12 TO ABOUT 24 CARBON ATOMS FROM A LIQUID MIXTURE CONSISTING ESSENTIALLY OF SAID ALKANOLS AND ALKANES AND MONO-OLEFINS OF SIMILAR BOILING POINTS WHICH COMPRISES ADDING TO SAID MIXTURE FROM ABOUT 0.25 TO ABOUT 20 PARTS BY WEIGHT OF A LOWER NITROALKANE HAVING UP TO THREE CARBON ATOMS PER MOLECULE PER PART BY WEIGHT OF SAID MIXTURE, SUBJECTING THE RESULTING MIXTURE TO AGITATION, THEREAFTER REDUCING THE TEMPERATURE OF SAID RESULTING MIXTURE TO ITHIN THE RANGE FROM ABOUT 35 TO ABOUT 55*F. UNTIL ALKANOLS CRYSTALLIZE FROM SOLUTION, SEPARATING SAID CRYSTALS FROM THE RESULTING MIXTURE AND STRIPPING THE SEPARATED CYRSTALS TO REMOVE RESIDUAL NITROALKANE AND ALKENES. 